Method of nitrating cellulose lacebacking fabrics



atented 15, 1949 UNITED STATES OFFICE MET-HGP QF NXTRATING CELLULOSELACE- .escrime FABRICS f Ne Brewing.

4 "Claims- 41 VThis invention relates to nitratedcellulose'fabfrics and methods for makingsucfh'fabrics. "More particularly, the fabrics of this invention vare especially adaptedfor use infthemanllfcture of lace and the like articles.

H eretofore, backing or ground .fabrics Which are to be used in the manufacture .of lace, 4have been .prepared kby nitrating cotton or other ,celjlulose fabrics yin nitric acid baths. The fabric resulting from such a procedure has lace `stitched thereon and the composite material is passed through a bath of caustic alkali. rThenitrated backing fabric YdisintegratesI in the caustic a1- kali, lleaving the lace structure which-is unimpelred bythe eeue'oealkali.v to bev removed from the bath.

The nitrated fabrics originally used Awere highly nemmeble due to their .high nitrogen content. In order to produce fabrics havingv a substantielly lower degree of inemmabilitv, the nitric acidlbaths were modified-by the 1a'dclitiorrof phosphoric acid. The rnitration of the-:fabrics was also vadjusted to materially reduceert-he nitrogen content -of :the nitrated fabric. The `fabrics so produced have nitrogen contents vof approximately Q.4'% 'to 113% by Weight.

The nitrated fabrics of loiv nitrogen content as described, present several diiiculti'es. One disadvantage relates to the time vintervals required for the nitrating procedure. AIt rhasfbeen neces. sary to leeve cotton fabrice .submerged in phosphoric acid modied nitrating Abaths .for periods extending from one halfhour to as much fas thirtyfsix hours in order to achieve the-required degree of nitration. Accordingly it is an object of this invention to produce .a nitrated :cellulose fabric by subjecting a cellulosefabric to the action of a phosphoric -acid modified nitrating bath 'wherein the 'time interval 'necessary to 'produce 'a predetermined degree of nitration is freduced to a fraction of that 'required in lproce-- dures already known inthe art.

`A further diculty attendant toithe use of the nitrated fabrics of low nitrogen .content `is their relatively low tensile strengths. Inasmuch as the nitrated fabrics are used in the manufacture of lace and the fabric is subjected to the various strains incident to its passage through the lace making machines, an adequate and uniform tensile strength is necessary. The nitrated fabrics having low nitrogen content (1.0% or less) are characterized by a relatively low and nonuniform tensile strength. Therefore, it is a further object of this invention to produce an improved nitrated cellulose fabric which shall rApplication J :mirar-y 24, '19217 Serial No. '$24,246

Fhave entier-m and relativen high tensile strength,

The nitrated fabrics of low nitrogen content lhave .a 'tendency to deteriorate lri .relatively ebert'time yduriee'e e- 'It'lia's lo en obse. ed that suchfabrioe Will .dsintegratewthill 'a [De oid of 'two to 'three months. Accordingly, afurther oeieet of this invention is toprodnoe kan improved nitrated .cellulose fabric which will with? Steed deterioration p rticularlrintheipresenee or agenteioromoting elnlo'stnde'nite period o timee Y Y Another object o fthie .invention-is the production of .an improved nitrated .Cellulose `fabrifciby means of 'a nitric acid-phosphoric aidfbatn wherein thermal vproduct shall-have a nitrogen content olf approximately-9% to 6G%by weight. Seele a itratetifebrle shell be fortifierk characterized by a low degree of lellemmabilty and yetis readily disintegrated lin alkali.

Still another object of this invention is to trate e cellulose by theuse of e nitric eeidephoa cherie eeielbath4 of predetermined concentration whereby .the-cellulose elbrfio may be. .peesedeon tinuously through the bath and yet resultl a -fnelfproeluet having the desired nitrogen content.

Other -obfieete of myinvention will in rpart be obvious iefpert'hereinafter pointed out.

'lt has been foune .their a cellulose faerie eueh as cheese cloth or `the like maybe nitrated to e nitrogen content of more than 1.9% and Vlese than ttl-0% efe-t Vproduce e `nitratelrl -feerie having a relatively high tensile strength as compared to fabrice nitrated .te e nitrogen content of less than It. has also. zbeen ffolltld that febriQS ine `the higher nitrogen cont-eet still retain the. property of disintegration in canette alkali es. Well as other alkaline baths. Furthermore .the eerlodef Atitration :considerably reduced een-leeres to that resulted in processes known nthenrt.. l

Accordingly there is provided, in accordance with thepresent invention, a nitratingfbethtwhich comprises a"-mixture ofxnitric acid and phosphoric acidwherein ne nitric acid .may v:constitute from aboutjQS/bi toffabont 69% by volume. The xphos: phoric acid content zof the bath may be from about 6G to about 40% by volume. Small amounts of sulfuric acid may be optionally kadded to the bath. The cellulose fabric is passed through the bath in a continuous manner, is removed from the bath, exposed to the air for an appropriate time interval and is nally washed with water andweak alkali solutions to neutralize excess acid.

ltions of mildew, tol' an By way of illustration and without limiting myself to this particular form of my invention, the following illustrates bath compositions and appropriate procedure which will give the desired results:

. Parts by volume Nitric acid-concentration about 97% 60 Phosphoric acidconcentration about 75%- 40 Cotton fabric was continuously passed through the bath at a temperature of 100110 F. The fabric had a contact period within the bath of approximately 0.5 minute. The nitrated fabric coming out of the bath was exposed to the airV for approximately 4.5 minutes and was then passed through successive washing solutions of water and weak alkali. The nitrated fabric thus produced had a nitrogen content of approximately 6.0%.

Parts by volume' Nitric acid-concentration about 97% -40 Phosphoric acidconcentration about 75%-"60 Cotton fabric was passed through the bath in the manner described in Example 1. Using the same time intervals and temperatures, the final product had a nitrogen content of approximately 2.0%.

In both of the above examples sulfuric acid may be optionally added to the baths.

The temperatures indicated in the above examples may be varied with a corresponding variation in the time intervals of nitration and exposure in air, providing the final product has a nitrogen content of between 2.0% and 6.0% by weight.

A cotton fabric nitrated in accordance with the procedures outlined above and having a nitrogen content of 4.01 was tested for its tensile strength and showed a value of 23 pounds per inch.

Similar cotton fabrics which had been nitrated to nitrogen contents of V1.0% or less were also tested and showed tensile strengths of approximately 50% to 75% less than the tensile strengths of nitrated fabrics having nitrogen contents above 2.0%.

The nitrated cellulose fabrics of this invention 'are also characterized by a high degree 0f resistance to mildew. Upon exposure of the fabric to conditions of mildew it was noted that there was no decrease in tensile strength as compared to the tensile strength of the unexposed fabric.

The nitrated fabrics of this invention are stable during storage periods of almost indefinite length. In the case of nitrated cellulose fabrics of low nitrogen content (1% or less) it has been observed that they fail to stand up over a period of time and disintegrate while in storage within two (2) or three (3) months.

It was further determined that the nitrated cellulose fabrics of this invention are non-toxic and do not irritate the human skin upon contact therewith. Y Y

It will thus be seen that there is provided a product and a method for manufacturing the same in which the several objects of this invention are achieved and which is well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and asvarious changes might to made in the embodiment above set forth, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not in a limiting sense.

Having thus describedmy invention, I claim as new and desire to secure by Letters Patent:

1. The process of producing lace backing fabric comprising treating natural cellulose, open meth fabric with mixed acid comprising from 60 to ,10 parts by volume 97% nitric acid and from {40 to 60 parts by volume 75% phosphoric acid for about 0.5 minute and exposing the treated fabric 1 to air forabout 4.5 minutes.

fabric through a bath comprising a mixture of 50 parts by volume of 97% nitric acid and 40 parts by volume of 75% phosphoric acid for about 0.5 minute, exposing the treatedV fabric to'air for about 4.5 minutes and washing the treated fabric with water and dilute alkali.

3.V In the process of forming lace backing fabric, the steps of passing natural cellulose, open mesh fabric through a bath comprising from 60 to 40 parts by volume of 97% nitric acid and from 40 to 60 parts by volume of 75% phosphoric acid, retaining the fabricV in the bath for about 0.5 minute, removing the fabric from the bath and permitting the nitrating action to continue for about 4.5 minutes and removing the unreacted acids from the fabric.

4. In the process of nitrating natural cellulose open mesh, lace backing fabric, the steps of continuously passing the fabric through a bath comprising 40 to 60 parts by volume of 97% nitric 'acid and 60 to 'l0 parts by volume of 75% phosphoric acid for a time interval of approximately 0.5 minute, withdrawing the nitrated fabric from the bath and exposing it to air for a time interval of approximately 4.5 minutes and neutralizing the excess acid in said fabric by washing with water and dilute alkali, the said fabric having a nitrogen content of from about 2.0% to about 6.0% by weight.

. JOSEPH DAILOW.`

REFERENCES CITED rhe following references are of record in the file of this patent:

UNITED YSTATES PATENTS Number Name Date 1,384,802V Miles et al. Oct. 25, 1932 2,092,749 Bradshaw Sept. 14, 1937 2,302,107 Datlow Nov. 17, 1942 OTHER REFERENCES 

